1. Field of the Invention
The present invention relates to a work vehicle having a diesel engine installed in a rear portion of a vehicle frame. The vehicle has a system that improves exhaust component cooling.
2. Description of Related Art
In order to improve and resolve the environmental concerns of recent years, exhaust gas regulations have been toughened for diesel engines and the like. In work vehicles such as construction or agricultural machinery, various technologies have been developed which reduce particulate matter contained in exhaust gas so as to comply with such exhaust gas regulations. For example, instead of a conventional muffler, an exhaust gas purification device collecting particulate matter contained in exhaust gas may be mounted to a work vehicle. The exhaust gas purification device passes the exhaust gas through a diesel particulate filter (hereafter referred to simply as DPF) installed therein to collect the particulate matter. The collected particulate matter accumulates gradually in the DPF of the exhaust gas purification device, and so in order to prevent the DPF from clogging and prevent an increase in air resistance of the exhaust system, the particulate matter must be burned off and the DPF renewed. Therefore, an outer surface of the exhaust gas purification device housing the DPF must be configured to avoid being excessively cooled, and an exhaust pipe must be effectively cooled so as to reduce a temperature of the exhaust gas discharged to the exterior from the exhaust gas purification device.
A work vehicle disclosed in Japanese Patent Laid-open Publication No. 2012-026326 is configured as a riding mower having a mower unit arranged below a vehicle frame between left-right pairs of front and rear wheels, a driver's seat arranged at a center portion of the vehicle frame, an engine compartment covered by a hood formed at a rear portion of the vehicle frame, and an engine and engine components arranged within the engine compartment. The engine is a diesel engine having a radiator and a cooling fan provided on a front side. A DPF (exhaust gas purification device) purifying engine exhaust gas is arranged at a position rearward and above the diesel engine, and an air cleaner is provided at a position above the diesel engine. The exhaust gas flowing in from a left front side of the DPF is discharged through a short exhaust pipe which extends horizontally further toward the rear of the vehicle from an exhaust outlet on a right rear side of the DPF and opens toward the rear of the vehicle. The shortness of the exhaust pipe discharging the final stage of the exhaust gas is a measure to prevent the vehicle body from increasing in length; however, when the exhaust pipe is insufficiently cooled, exhaust gas having a comparatively high temperature may be discharged from the exhaust outlet.
In a riding mower disclosed in Japanese Patent Laid-open Publication No. 2013-209949, which has a similar format, in order to ensure an adequate length for an exhaust pipe, exhaust gas exiting an exhaust gas purification device flows through an exhaust passage, which extends forward and upward from the exhaust gas purification device, after which the exhaust passage extends forward of and above the exhaust gas purification device in a transverse direction of the vehicle until it passes the diesel engine, and further extends along a side wall of the diesel engine so as to descend toward the front, after which the exhaust passage reverses course and extends rearward along the side wall of the diesel engine to terminate at an exhaust outlet. With such an exhaust pipe layout, space above the rear portion of the engine and space beside a rear half of the engine is occupied by the exhaust pipe. In particular, a flow cross-sectional area of the exhaust pipe close to the exhaust outlet is large, and therefore the required space beside the rear half of the engine is larger. As a result, a width of the hood increases.
In view of the above circumstances, an improved layout of an exhaust pipe between an exhaust gas purification device and a final stage exhaust gas exhaust mouth is desired within a narrow engine compartment.